Traveling wave tube system



United States Patent 2,888,649 Patented May 26,1959

TRAVELING WAVE TUBE SYSTEM Edward C. Dench, Needham, and Albert D. LaRue, Lexington, Mass., assignors to Raytheon Manufacturing Company,Waltham, Mass., a corporation of Delaware Application January 31, 1956,Serial No. 562,472

12 Claims. (Cl. 332-17) This invention relates to a system forincreasing the power obtainable with traveling wave oscillators and,more particularly, to a system employing two or more tunable travelingWave oscillators whose frequency of operation is reasonably closetogether, wherein a signal generated by each oscillator other than theone connected to the output load is injected as an input signal intoanother'one' of said oscillators.

Traveling'wave oscillators are known which include a periodic slow wavepropagating structure which has the properties of an electrical filter,that is, waves can be propagated over the pass band of the structure.Such tubes make use of the interaction between an electron beam movingalong paths adjacent the periodic structure and the electromagneticfield of the wave guided by said periodic structure.

The electromagnetic field along such a structure may be considered toconsist of an infinite number of superimposed traveling waves or spaceharmonics each having phase velocities V given by where A is the pitchor length of one network section, is the phase shift per section, and nis the number of the space harmonic, for example, n=0, :1, :2, etc. Thephase velocity of the space harmonics may be either positive ornegative, depending upon the value of n. When V has a positive value,the phase velocity is in the same direction as the energy or groupvelocity and the corresponding phase harmonics may be referred to asforward waves. On the other hand, when V is negative, the phase velocityis in a direction opposite to the energy or group velocity and thecorresponding waves then are referred to as negative space harmonics orbackward waves.

If, for example, an electron beam flows in the direction of one of thesebackward waves at a velocity substantially equal to the phase velocityof the backward wave, interaction will take place between the beam andthe traveling wave and a progressive modulation of the electron beam isobtained such that energy will be transferred from the electron beam tothe electromagnetic field and the energy given to the backward wave willbe transferred along the periodic structure toward the electron beamsource. When the electron beam current is in excess of a criticalcurrent where oscillations can begin and when the electron beam velocityis substantially equal to the velocity of the one of the spacebarmonies, such as a backward wave, oscillations will be generatedwithin the tube; these oscillations will propagate along the periodicstructure and may be extracted at one end of the periodic structure.

In a first type of backward wave oscillator, the electron beam isaccelerated by an electric field associated with the electron gun and,in some instances, in an axial magnetic field for focusing the electronbeam. In a second type of a backward wave oscillator the beam movesthrough a magnetic field which is arranged transversely to an electricfield which may be produced by a voltage supplied between the periodicdelay structure and either the electron source or an auxiliary negativeelectrode. In the first type of oscillator, the electron beam velocityis dependent upon the magnitude of the voltage which causes accelerationof the electrons; in the second type, the average forward electron beamvelocity is directly a function of the aforesaid voltage and is directlydetermined by the ratio of the electric and mag netic field strengths.

Such oscillators may be tuned over a wide range of frequencies byvarying the electron beam velocity through adjustment of said voltage,as well as by adjustment of the transverse magnetic field strength inthose oscillators employing a transverse magnetic field.

In accordance with the invention, two traveling wave, oscillators whosefree running frequencies are relatively close together may be connectedin tandem, that is, with the output from the first or driver tubeconnected as an input signal to the second or driven tube at the end ofthe driven tube remote from its output end. In this manner, it has beenfound in practice that the power output derived from the driven tube maybe greater than the combined power output of both tubes operatingindependently. In other words, the efiiciency of the driven or lockedoscillator may be increased over the efiiciency of the same oscillatorwhen operating alone. The oscillators can be made voltage tunable over arelatively wide range and the tuning means of the oscillators may beganged or otherwise arranged so that the frequency of oscillation of thedriven oscillator can be locked to that of the incoming signal derivedfrom the driver oscillator over the entire tuning range.

The invention is not limited, however, to a system consisting of twooscillators. Any number of oscillators of comparable frequency,depending upon the power and requirements of the system, can be cascadedto form a chain of injection-locked units; each oscillator will thenoperate, in effect, as a locking or driver oscillator for the nextoscillator in the chain. The frequency of the last oscillator of thechain which is connected to a utilization circuit is lockedsubstantially to that of the first oscillator in the chain. It has beenfound in practice that the power output obtained from the last stage ofthe chain may be greater than the sum of the power outputs of all theoscillators in the chain. For example, if three oscillators areconnected in tandem in the manner described, the power output, in someinstances, is greater than three times the power output of each tubeoperating independently.

The systems according to the invention may be either amplitude orfrequency modulated by application of an amplitude modulating signal ora frequency modulating signal to one or more of the oscillators.Amplitude modulation of a limited range may also be achieved concurrently with frequency modulation by applying a frequency modulatingsignal to less than all of the oscillators.

The systems according to the invention are quite reliable since, if oneor more of the tubes in the chain should fail, owing for example to adefective electron gun, energy will continue to propagate along thedelay structure of the faulty tube or tubes, so long as at least one ofthe tubes is operating satisfactorily. Even if the driver oscillator ina two-tube system should fail, it would act as a termination for theother tube, and energy, albeit at reduced power, may be derived from theoutput end of the driven tube.

Reflections within the system may be minimized by means of electricalattenuation inserted either externally of the tube or within the tubesthemselves.

This invention further contemplates the use of a high frequencygenerator other than a backward wave traveling wave oscillator forsupplying the initial locking signal. In systems which are required tooperate over a range of frequencies, however, it is necessary to insurethat the frequency of the locking signal tracks with that of thetraveling wave oscillator or oscillators in the system.

Other objects and features of this invention will be understood moreclearly and fully from the following detailed description of theinvention with reference to the accompanying drawings wherein:

Fig. l is a central cross-sectional view, partly in elevation, of anembodiment of a traveling wave oscillator tube which may be utilized inthe system according to the invention;

Fig. 2 is a detail view of a portion of the anode assembly of thetraveling wave oscillator tube of Fig. 1;

Fig. 3 is a section view taken along the line 3-3 of Fig. 1;

Fig. 4 is a fragmentary view of a portion of the electron gun mountingassembly attached to an elongated electrode of the traveling waveoscillator tube of Fig. 1;

Fig. 5 is a schematic diagram of a first embodiment of aninjection-locked traveling wave oscillator system according to theinvention;

Fig. 6 is a schematic diagram of a modification of the system shown inFig. 5;

Fig. 7 is a diagrammatic view of a further embodiment of the systemaccording to the invention in which more than two oscillator tubes areemployed;

Fig. 8 is a diagrammatic view of a further modifica tion of the systemaccordin to the invention illustrating the use of oscillator tubeshaving no transverse magnetic field; and

Fig. 9 are curves illustrating certain principles of operation of theinvention.

Referring now to Figs. 1 to 4, a traveling wave tube oscillator is shownwhich comprises an anode assembly 21 which includes a periodic slow waveenergy propagating structure or anode delay line 22, an elongatedelectrode 30, sometimes referred to as a sole, maintained negative withrespect to anode delay line 22, a lead-in assembly 40, an outputcoupling means 50, an electron gun mounting assembly 60 furtherincluding at least a cathode 61 and heater 62, an input coupling means76, and a transverse magnetic field-producing means 8@81, a portion ofwhich is indicated in Fig. l.

The anode assembly comprises a circular interdigital delay lineincluding a plurality of interdigital fingers or members 24 and 24 whichextend from oppositely disposed annular members 25 and 25, respectively.Members 25 and 25 are secured by screws 26 (see Fig. 2) to the shoulderportion of a cylindricai electrically conductive ring 27. The remainderof the anode assembly includes a pair of oppositely located cover plates28 and 29 hermetically sealed to ring 27.

The sole 3% consists essentially of a cylindrical block of material,such as copper, having a flange portion 37. A centrally located aperture31 is provided in the sole to permit connection of lead-in assembly 46and to allow for passage of external circuit-connecting leads in amanner to be shown subsequently.

Lead-in assembly 44) includes an electrically conductive cylindricalsleeve 42 which is inserted in an aperture in cover plate 28 and issecurely attached thereto. A section of cylindrical glass tubing 43interconnects metal sleeve 42 and a second metal sleeve 44. The otherend of sleeve 44 is provided with a glass seal 45 for sealing tube 24)after evacuation. Sleeves 42 and 44 preferably are constructed of amaterial having an expansion coefiicient closely approximating that oftubing 43. The

assembly 40 is arranged perpendicularly to cover plate 28 of tube 20 andfurther includes an elongated electrically conductive tubular supportingcylinder 46 which serves as the main support for sole 30. One end ofcylinder 46 is afiixed to the periphery of aperture 31 in sole 3%. Theother end of cylinder 46 contains an outwardly flared portion 47 whichis connected to the inner surface of sleeve 44. The necessary leads forthe electron gun are fed through supporting cylinder 46 and areinsulatedly supported therefrom by one or more glass beads 4-9.

The interdigital anode delay line 22 is arranged concentric with sole 30and is separated from the circumferential wall 33 of the sole to form aninteraction space through which the electron beam generated by theelectron gun passes. Anode delay line 22 may be terminated at one end byattenuation which may be in the form of an energy-dissipative material,such as iron, applied to the fingers.

The coaxial output coupling means 50 is sealed in an opening of wall 27of the anode and is impedance matched to the anode delay line 22. Theinner conductor 52 of coaxial output coupling means 50 is connected to afinger at or adjacent the end of the periodic anode delay line 22adjacent the electron gun.

Traveling wave tube 20 may be provided with a collector electrode 23,shown in Figs. 2 and 3, for intercepting electrons after one traversalof the arcuate inter action space. This collector electrode may take theform of a projection from the back wall 27 of the anode delay line 22.In some instances, however, the collector electrode may be omitted andthe electron stream made reentrant. Furthermore, the sole 30 may beeither primarily or secondarily electron-emissive.

The electron gun assembly for the tube of Fig. 1 includes cathode 61,heater 62, and auxiliary electrode 65, as shown in detail in Fig. 4. Thecathode 61 is shown, by way of example, as a rectangular body providedwith a circular bore 63 in which the heater 62 is inserted. Cathode body61 has at least the surface facing the interaction space 35 coated withan electronemissive material, such as a compound of barium. Cathode 61is positioned within a recess or slot 32 in the wall 33 of sole 30.Electrical connection to the cathode is made by way of a rigid,electrically conductive stake 66 which may be made of molybdenum andspot welded to one end of the cathode body. The cathode lead 48 isconnected to stake 66. One end of heater 62 is connected to the innerwall of the cathode body while the other end of the heater is attachedto a stake 67; stake 67 is insulatedly mounted by means of a bushing 64on the top face of sole 30, as shown clearly in Fig. 4. The heater lead19, shown in Fig. 1, is attached to stake 67.

The cathode 61 is supported by means of a flange 68 which may besecured, as by brazing, to the cathode body at one end, as shown in Fig.4, and attached, as by insulating screws (not shown) to a portion of thesole at the bottom of slot 32. Cathode 61 is insulated from sole 36 bymeans of an electrically insulated spacer 15. The auxiliary electrodewhich, in effect, is an accelerating anode serving to aid in theproduction of the desired electron beam trajectory, is supported fromsole by means of insulating screws 16 which pass through flange portion65 of auxiliary electrode 65 and into flange portion 37 of sole 30. Anelectrically insulating spacer 17 provides for electrical isolation ofthe auxiliary electrode 65 and sole 3%. Electrical connection is made toauxiliary electrode 65 by means of a stake 69 aflixed to one end of theauxiliary electrode and electrically in sulated from the sole by virtueof its passage through an aperture 18 in the sole. Lead 41 is attachedto stake 69.

A suitable electric field between anode and sole may be obtained bymeans of a voltage applied therebetween. The sole may be negativelybiased with respect to the cathode by means of a source 107 of voltageconnected between cathode leads 48 and tubular sleeve 46 by way ofsleeve 44. The cathode may, in some instances, be at the same potentialas the sole. Similarly, anode delay line 22 may be maintained at apositive potential relative to both sole and cathode by means of asource 105 of voltage connected between metal sleeve 42 connected inturn to the anode delay line and cathode lead 48. The auxiliaryelectrode 65 may be maintained at a positive potential relative to thecathode by means of a source 109 of voltage connected between leads 41and 48.

A uniform magnetic field transverse to the direction of propagation ofthe electron beam is provided either by a permanent magnet or anelectromagnet having cylindrical pole pieces 80 and 81 radiallypositioned on or adjacent the tube. Pole piece 80 is apertured toreceive the leadin assembly 40 and pole piece 81 is apertured tomaintain symmetry of the magnetic field. The flux lines should beconcentrated in the interaction space 35 between sole 30 and cylindricalanode delay line 22. By proper adjustment of the magnitude and polarityof the magnetic and electric fields, the electron beam may be made tofollow a circular path about interaction space 35 under the combinedinfluence of these transversely disposed fields.

The radio frequency energy generated in the interaction space 35traveling along anode delay line 22 sets up a high frequencyelectromagnetic field which may be analyzed as a series of spaceharmonics, some of which travel in one direction (clockwise) along theanode structure, and others of which travel counterclockwise, and all ofwhich travel with different phase velocity. If the electron beam issynchronized with the proper space harmonic, interaction of the beam andthis space harmonic will result in the production of oscillations withinthe tube. The energy travels toward the electron gun and is extracted atthe gun end of anode delay line 22 by way of the coaxial output line 50.

Traveling wave tube 20 further includes an input coupling assembly 70comprising inner conductor 71 and an outer conductor 72 coaxiallyarranged with respect to one another. The inner conductor 71 isconnected to one of the fingers at or adjacent the end of the anodedelay line 22 electrically remote from the electron gun, while the outerconductor 72 may be attached to the cylindrical wall 27 of anodeassembly 21.

The input coupling means 70, as well as output coupling means 50, neednot be coaxial; for example, the energy may be coupled to or from theanode delay line 22 by means of a wave guide.

Referring now to Fig. 5, two backward wave oscillators, such asdescribed in Figs. 1 to 4, are represented by the reference numerals 20aand 20b. These oscillators are indicated schematically in Fig. 5 aslinear, for reasons of simplicity. The systems of the invention are notrestricted to any particular configuration of oscillator 2, however, andoscillators of the linear type may be used in accordance with thisinvention. Each oscillator tube includes a periodic slow wavepropagating network for anode delay line 22 shown, by way of example,only as an interdigital line having a plurality of interdigital fingers,or elements, such as elements 24 and 24 of the device shown in Figs. 1to 4, each of which is connected together for direct current. The delayline 22 need not be of the interdigital type, however, but may be anysuitable periodic delay structure such as a helix, discloaded Waveguide, or the like. Each tube includes an elongated electrode or sole30, which is maintained negative with respect to delay line 22 by meansof the unidirectional source of voltage 105 and the unidirectionalsource of voltage 107 connected between the anode delay line 22 and sole30. An electric field thereby is produced between anode delay line 22and sole 30.

Each tube further includes an electron gun comprising a cathode 61 andan auxiliary electrode (accelerating anode) 65 for directing a beam ofelectrons 100 substantially parallel to the anode delay line 22 underthe influence of the electric field and a magnetic field transversethereto. The electron beam may impinge on a collector electrode 23 whichmay be maintained at the same potential as the anode delay line 22 or atsome potential positive relative to the cathode. In some instances, thecollector 23 may be omitted and the electron beam allowed to impingeupon the delay line 22; since the region remote from the electron gun isnormally an attenuating region, the impingement of the electron beamupon the anode delay line usually is of no consequence.

Tuning of each oscillator may be accomplished by varying the voltagebetween delay line 22 and sole 30; in practice, this voltage variationmay be achieved by connecting a potentiometer 104 across voltage source105 in a manner such as indicated in Fig. 6. Tuning of each oscillatoralso may be accomplished by varying the magnetic field strength, eitherby varying the position of the magnet pole pieces, in the case of apermanent magnet, or by varying the electric current, in the case of anelectromagnet having a coil surrounding the core. Variation of bothelectric field and the magnetic field simultaneously, of course, ispossible.

In the diagram of Fig. 5, the oscillators are of a transverse magneticfield type in which the electron beam is under the combined influence ofan electric field and a magnetic field transverse to the electric field;the electron beam is mutually perpendicular to the direction of bothfields. This magnetic field is indicated by the letter B and thedirection of the field is indicated by a cross within a circle. In tubesof this type, the electron beam velocity is proportional to the ratio ofthe anode delay line-to-sole voltage and the magnetic field strength(flux density). This invention, however, is applicable equally to anoscillator in which an accelerated electron beam travels in theinteraction space adjacent the anode delay line and in which as amagnetic field, if used at all, is an axial field which serves only tofocus the electron beam. In an oscillator of this type, shownschematically, for example, in Fig. 8, the electron beam velocity isproportional to the square root of the voltage through which theelectrons have been accelerated.

Energy is removed from the end of the periodic anode delay structure 22adjacent the cathode 61 by means of an output coupling device 50 such asalready described in Figs. 1 to 4. Amplitude modulation of eachoscillator may be accomplished by means of an amplitude modulatingsignal from a source 112 applied to the circuit containing auxiliaryelectrode 65 across terminals 113; terminals 113 are connected,respectively, to one end of the bias supply 109 and cathode 61.

In order to achieve proper locking of the oscillators, itis essentialthat the frequency of operation of each tube, running by itself, be nearthat of the other tube or tubes, for example, within about 5%. In orderto insure that the nominal free running frequencies of operation of thevarious oscillators do not differ appreciably, it may be necessary tocompensate for individual differences in construction and in electrodevoltages of the oscillators by means of a bias voltage source 107connected between cathode 61 and sole 30. The bias can be adjusted oneach oscillator until the operating frequencies are substantially equal.If the devices have substantially identical characteristics, the biassources may, of course, be omitted. It has been found that, in manyinstances, the space charge conditions for a tube being driven and thesame tube running freely are slightly dilferent. This may be anotherreason for utilizing separate bias power supplies for the various tubes.

The driven oscillator tube 20b must be provided with an input couplingdevice 70 which is coupled to the periodic anode delay structure 22adjacent the end remote from its cathode. The output coupling device maybe similar in construction to that of the input coupling device 50 andmay be coupled to the anode delay structure 22 in the same manner.Attenuation may be introduced at the end of tube 20b remote from theoutput end, in order to reduce reflections from the driven oscillator 2%back through the system into the driver oscillator 20a, and also to takecare of reflections which may arise at the interconnection between thetubes. Furthermore, the use of attenuation eliminates frequencydiscontinuities in the oscillator during tuning. This attenuation maytake form or" a thin coating of lossy material such as graphite appliedto the end of the delay line 22, as by spraying a solution of graphitemixed with a suitable binder, or by coating the delay line with iron byelectroplating techniques. The attenuation is indicated in Fig. 5 and insucceeding figures of the drawing by cross-hatching or oblique linesdrawn through the anode delay line 22.

Energy generated by the driving oscillator 28a is re moved therefrom bymeans of output coupling device 58 and is applied to the input couplingdevice '70 of the driven oscillator Ebb by way of a transmission line111 which may be, for example, a coaxial line. The driver oscillatortube 20a, like the driven oscillator 20b, may be provided with acoupling device 70 coupled to the end of the anode delay line 22 remotefrom its cathode. This attenuation may take the form of a thin coatingof external lossy termination 115 which is of such impedance as toreduce substantially reflections within the tube Zita. Externalattenuation may also be introduced in the line 111 interconnecting thetwo oscillators. As shown in Fig. 6, internal attenuation may beintroduced in the driver tube 20a rather than external attenuation. Theadvantage accruing from the use of external attenuation isstandardization of tubes, whereas the advantage of internal attenuationis that somewhat better impedance matching may be achieved with internalattenuation than with external attenuation. It should be noted, however,that the invention does not necessarily contemplate the use ofattenuation; in some instances, the reflected energy may be ofinsuflicient magnitude to prove troublesome.

The advantages of injection-locked backward-wave oscillator operation isclearly shown in the curves of Fig. 9, in which the relationship betweenrelative power and relative frequency is indicated. The power obtainedby the use of a single oscillator operating independently is indicatedby the lower curve 152, while the power obtained when two oscillatorsare cooperating in the manner described in Fig. 6 is indicated by theuppermost curve 150. It will be noted in this case that the powerobtained by the use of two oscillators utilizing the injection lockingprinciple according to the invention is more than double the powerobtained by using a single oscillator only.

In Fig. 6, a modification of the system of Fig. 5 is shown wherein acommon power supply 105 is used for both tubes, and wherein means areprovided for frequency modulating the system. Voltage tuning of theoscillators 28a and 26/) may be accomplished simultaneously by varyingthe position of the arm of potentiometer 104 connected across battery105. Frequency modulation is accomplished by a modulating signal from amodulating source 118; the modulation signal may be inserted in one ofthree positions, that is, between terminals 120, between terminals 122,or between terminals 124. Jumpers 121 are provided across the unusedterminals. 1f the modulation signal from source 118 is inserted acrossterminals 120, that is, in the circuit be tween anode 22 and sole 30 ofboth driver tube 20a and driven tube 2%, as shown in Fig. 6, frequencymodulation may be eflected with substantially no amplitude modulation,since the frequency of both oscillators is being varied simultaneouslyand the oscillators are in step, frequency-wise. If the modulationsignal is inserted between terminals 122, that is, in the circuitbetween the anode and sole of the driver tube 20a, the driven tube 201)will follow over the locking range,

that is, over a narrow range of frequency, for example, about 5 to 10percent removed from the nominal freerunning frequency of eachoscillator; the power output, however, is changed in such a case.Finally, if a moduiation signal is introduced between terminal 124, thatis, in the circuit between anode and sole of the driven tube 2%, theoutput frequency of the system is substantially equal to the frequencyof the driver tube within the locking range; in this case, also, thepower output will vary with the signal applied to terminals 124.

Since the application of a modulation signal between terminals 122 orbetween terminals 124- produces some amplitude modulation, analternative method to that of provided. However, the percentageamplitude modula tion which may be achieved by applying a modulationsignal between the sole and anode delay line is less than thatattainable by applying an amplitude modulation signal to the electrongun, in the manner shown in Fig. 5. Although the attenuation is shown inFig. 6 as being inserted in the delay line of the driver tube 20a, it ispossible to insert the attenuation externally, as shown in Fig. 5.

In Fig. 7, a system is illustrated which incorporates more than twooscillators, that is, wherein several injection-locking units may becascaded. If several oscillators are thus cascaded, the power outputobtained from the last oscillator in the chain and available forutilization is greater than the sum of the power outputs of all of theoscillators when each oscillator is acting independently. The outputfrom each oscillator is applied to the input of the next oscillator sothat each oscillator, save the one to which the output load is coupled,acts as a driver for the one following. For reasons already mentioned,internal attenuation may be provided at the input end of the delay line,that is, at the end remote from the output end, in the case of theinitial driver tube. As previously explained, attenuation inserted inthe delay line of the initial driver tube Zita may be either internal orexternal. When several tubes are utilized, the energy reflected, in theabsence of attenuation, may well be considerable and may be greater thanthe power-handling capability of one or more of the tubes, particularlythe initial driver tube 20a.

As in the system of Fig. 6, a common power supply may be used in thesystem of Fig. 7 in the circuit between the sole 3d and the anode delayline 22 of all of the tubes. Furthermore, a common cathode-to-sole powersupply 107 and a common auxiliary electrode-tocathode power supply 109may be used for all tubes. It is possible, of course, to use a separatepower supply for each tube.

As previously mentioned, this invention is not limited to oscillatortubes using a transverse magnetic field. In Fig. 8, a system isillustrated which utilizes a backward oscillator without a transversemagnetic field. Such tubes may include a slow wave propagating networkin the form of a helix 22 through which an electron beam is directed bymeans of an electron gun including a cathode 61, a control grid 130, andan auxiliary anode 132, and, some cases, a beam focusing meanscomprising an axially arranged coil 135 for producing a longitudinalmagnetic field. The electron beam impinges on a collec tor electrode 23after traversing the length of helix 22. The collector is maintainedpositive with respect to the cathode 61 by means of a unidirectionalhigh voltage source, such as a battery 1615. In some cases, a separatecollector circuit may be omitted. The voltage source can be connecteddirectly to the anode delay line or helix 22. The auxiliary anode 132 ismaintained at some fixed positive voltage relative to the cathode bymeans of an electron voltage source 147 whose negative terminal isconnected to the cathode. Amplitude modulation is achieved by varyingthe negative control grid voltage applied between the control grid andthe cathode 61;

this may be accomplised by a potentiometer 138 shunting voltage source140. As the arm of potentiometer 138 1s moved upward, the control gridvoltage, relative to the cathode, becomes more negative, and the poweroutput of the oscillator tube can be decreased; as the potentiometer armis moved downward, of course, tube power is increased. Tuning with eachoscillator is accomplished by varying the voltage between the helix (orcollector) and the cathode. This voltage may be varied by adjustment ofthe arm of potentiometer 145 shunting the high voltage source 105.

Although the oscillator shown in Fig. 8 includes a helix, it is possibleto employ an interdigital line such as shown in Figs. to 7.

This invention is not limited to the particular details of construction,materials and processes described, as any equivalents will suggestthemselves to those skilled in the art. It is accordingly desired thatthe appended claims be given a broad interpretation commensurate withthe scope of the invention within the art.

What is claimed is:

1. In combination, a traveling wave oscillator including an electronsource, means for directing a beam of electrons from said source alongan extended path, a pcriodic slow wave energy propagating structurepositioned adjacent said path in which there is induced by the electronbeam an electromagnetic wave traveling in a direction opposite that ofthe electrons to generate oscillatory energy of a predeterminedfrequency, an output means coupled adjacent the end of said structurenearer said electron source for removing energy propagating along saidstructure, an input coupling device coupled to said structure adjacentthe end thereof remote from said electron source, and means forsupplying an external signal of substantially said predeterminedfrequency to said input coupling device.

2. In combination, a first traveling Wave oscillator, a second travelingwave oscillator, each including an electron source, means for directinga beam of electrons from said source along an extended path, a periodicslow wave propagating structure positioned adjacent said path in whichthere is induced by the electron beam an electromagnetic wave travelingin a direction opposite that of the electrons to generate oscillatoryenergy, and an output means coupled adjacent the end of each of saidstructures nearer said electron source for removing energy propagatingalong the corresponding periodic structure, an input coupling devicecoupled to the structure of said second oscillator adjacent the endthereof remote from the corresponding electron source, and means forinterconnecting the output means of said first oscillator to the inputcoupling device of said second oscillator, said second oscillator beinglocked in frequency to that of said first oscillator in response toenergy received from said first oscillator by way of saidinterconnecting means.

3. In combination, a first traveling wave oscillator, a second travelingwave oscillator, each including an electron source, means for directinga beam of electrons from said source along an extended path, a periodicslow wave propagating structure positioned adjacent said path in whichthere is induced by the electron beam an electromagnetic wave travelingin a direction opposite that of the electrons to generate oscillatoryenergy, means for providing an electric field in the region of saidstructure, an output means coupled adjacent the end of each of saidstructures nearer said electron source for removing energy propagatingalong the corresponding periodic structure, means for varying thefrequency of said oscillators simultaneously over a predeterminedfrequency range in response to variations in said electric field, saidoscillators operating individually at substantially the same frequency,an input coupling device coupled to the structure of said secondoscillator adjacent the end thereof remote from the correspondingelectron source, means for interconnecting the output means of saidfirst oscillator to the input coupling device of said second oscillator,said second oscillator being locked in frequency to that ofsaid firstoscillator over said frequency range in response to energy received fromsaid first oscillator by way'of said interconnecting means.

4. In combination, a multiplicity of traveling wave oscillators, eachincluding an electron source, means for directing a beam of electronsfrom said source along an extended path, a periodic slow wavepropagating structure positioned adjacent said path in which there isinduced by the electron beam an electromagnetic wave traveling in adirection opposite that of the electrons to generate oscillatory energy,and an output means coupled adjacent the end of said structure nearersaid electron source for removing energy propagating along saidstructure, said oscillators being adapted to operate individually atsubstantially the same frequency, said oscillators other than the firstoscillator including an input coupling device coupled to a correspondingone of said structures adjacent the end thereof remote from its electronsource, and means for interconnecting the output means of each of saidoscillators other than the last oscillator to the input coupling deviceof the immediately succeeding oscillator, each of said oscillators otherthan said first oscillator being locked in frequency to that of theimmediately preceding oscillator in response to energy received from theimmediately preceding oscillator by way of said interconnecting means.

5. In combination, a multiplicity of traveling wave oscillators, eachincluding an electron source, means for directing a beam of electronsfrom said source at a given average velocity along an extended path, aperiodic slow wave propagating structure positioned adjacent said pathin which there is induced by the electron beam an electromagnetic wavetraveling in a direction opposite that of the electrons to generateoscillatory energy, and an output means coupled adjacent the end of eachof said structures nearer said electron source for removing energypropagating along said structure, means for varying the frequency ofsaid oscillators simultaneously over a predetermined frequency range inresponse to variations in said average velocity, said oscillatorsoperating individually at substantially the same frequency, saidoscillators other than the first oscillator including an input couplingdevice coupled to a corresponding one of said structures adjacent theend thereof remote from its electron source, and means forinterconnecting the output means of each of said oscillators other thanthe last oscillator to the input coupling device of the immediatelysucceeding oscillator, each of said oscillators other than said firstoscillator being locked in frequency to that of the immediatelypreceding oscillator in response to energy received from the immediatelypreceding oscillator by way of said interconnecting means.

6. In combination, a multiplicity of traveling wave oscillators, eachincluding an electron source, means for directing a beam of electronsfrom said source along an extended path, a periodic slow wavepropagating structure positioned adjacent said path in which there isinduced by the electron beam an electromagnetic wave traveling in adirection opposite that of the electrons to generate oscillatory energy,and an output means coupled adjacent the end of each of said structuresnearer said electron source for removing energy propagating along saidstructure, means including a single source of voltage connected betweeneach of said electron sources and a corresponding one of said structuresfor providing an electric field therebetween, means for producing amagnetic field in each oscillator transverse to said electric electronsource, and means for interconnecting the output means of each of saidoscillators other than the last oscillator to the input coupling deviceof the immediately succeeding oscillator, each of said oscillators otherthan said first oscillator being locked in frequency to that of theimmediately preceding oscillator in response to energy received from theimmediately preceding oscillator by Way of said interconnecting means.

7. In combination, a multiplicity of traveling Wave oscillators, eachincluding an electron source, an auxiliary element located adjacent saidelectron source, means for directing a beam of electrons from saidsource along an extended path, a periodic slow Wave propagatingstructure positioned adjacent said path in which there is induced by theelectron beam an electromagnetic wave traveling in a direction oppositethat of the electrons to generate oscillatory energy, and an outputmeans coupled adjacent the end of each of said structures nearer saidelectron source for removing energy propagating along said structure,means including a common source of voltage applied to a correspondingone of said structures for providing an electric field therebetween,means for producing a magnetic field in each oscillator transverse tosaid electric field, means for varying the frequency of said oscillatorssimultaneously over a predetermined frequency range in response tovariations in at least one of said fields, said oscillators operatingindependently at substantially the same frequency, said oscillatorsother than the first oscillator including an input coupling devicecoupled to a corresponding one of said structures adjacent the endthereof remote from its electron source, means for interconnecting theoutput means of each of said oscillators other than the last oscillatorto the input coupling device of the immediately succeeding oscillator,said oscillator other than said first oscillator being locked infrequency to that of the immediately preceding oscillator in response toenergy received from the immediately preceding oscillator by Way of saidinterconnecting means, and means for applying an amplitude modulatingvoltage to said auxiliary element to control the amplitude of the energyextracted from the last of said oscillators.

8. In combination, a multiplicity of traveling Wave oscillators, eachincluding an electron source, an auxiliary element located adjacent saidelectron source, means for directing a beam of electrons from saidsource along an extended path, a periodic slow wave propagatingstructure positioned adjacent said path in which there is induced by theelectron beam an electromagnetic Wave traveling in a direction oppositethat of the electrons to generate oscillatory energy, and an outputmeans coupled adjacent the end of each of said structures nearer saidelectron source for removing energy propoagating along said structure,means including a common source of voltage applied to a correspondingone of said structures for providing ar electric field therebetween,means for producing a rnrgnetic field in each oscillator transverse tosaid electric field, means for varying the frequency of said oscillatorssimultaneously over a predetermined frequency range in response tovariations in at least one of said fields, said oscillators operatingindependently at substantially the same frequency, said oscillatorsother than the first oscillator including an input coupling devicecoupled to a corresponding one of said structures adjacent the endthereof remote from its electron source, means for interconnecting theoutput means of each of said oscillators other than the last oscillatorto the input coupling device of the immediately succeeding oscillator,said oscillator other than said first oscillator being locked infrequency to that of the immediately preceding oscillator in response toenergy received from the immediately preceding oscillator by Way of saidinterconnecting means, means for applying an amplitude modulatingvoltage to said auxiliary element to control the amplitude of the energyextracted from the last of said oscillators, and

means for applying a frequency modulating signal to said structure of atleast one of said oscillators.

9. In combination, a multiplicity of traveling Wave oscillators, eachincluding an electron source, means for directing a beam of electronsfrom said source along an extended path, a periodic sloW wavepropagating structure positioned adjacent said path in which there isinduced by the electron beam an electromagnetic Wave to generateoscillatory energy, and an output means coupled to each of saidstructures for removing energy propagating along said structure, saidoscillators being adapted to operate individually at substantially thesame frequency, said oscillators other than the first oscillatorincluding an input coupling device coupled to a corresponding one ofsaid structures, means for interconnecting the output means of each ofsaid oscillators other than the last oscillator to the input couplingdevice of the immediately succeeding oscillator, each of saidoscillators other than said first oscillator being locked in frequencyto that of the immediately preceding oscillator in response to energyreceived from the immediately preceding oscillator by way of saidinterconnecting means.

10. In combination, a first voltage tunable traveling wave oscillatorhaving an output terminal, a second voltage tunable traveling waveoscillator having an input terminal and an output terminal, saidoscillators being adapted to operate individually at substantially thesame frequency, and means for interconnecting the output terminal ofsaid first oscillator and the input terminal of said second oscillator.

11. In combination, a multiplicity of voltage tunable traveling Waveoscillators, each including an electron source, means for directing abeam of electrons from said source at a given average velocity along anextended path, a periodic slow wave propagating structure positionedadjacent said path in which there is induced by the electron beam anelectromagnetic wave, an output means coupled to said structure, and aninput coupling device coupled to said structure, means forinterconnecting the output means of each of said oscillators other thanthe last oscillator to the input coupling device of the immediatelysucceeding oscillator, and means for deriving an output for utilizationfrom the output means of the last of said oscillators.

12. In combination, a multiplicity of voltage tunable traveling Waveoscillators, each including an electron source, means for directing abeam of electrons from said source at a given average velocity along anextended path, a periodic slow Wave propagating structure positionedadjacent said path in which there is induced by the electron beam anelectromagnetic wave, an output means coupled to said structure, and aninput coupling device coupled to said structure, means forinterconnecting the output means of each of said oscillators other thanthe last oscillator to the input coupling device of the immediatelysucceeding oscillator, means for deriving an output for utilization fromthe output means of the last of said oscillators, and means for tuningall of said oscillators concurrently.

References Cited in the file of this patent UNITED STATES PATENTS2,611,832 Lapostolle Sept. 23, 1952 2,616,990 Knol et al Nov. 4, 19522,653,270 Kompfner Sept. 22, 1953 2,702,370 Lerbs Feb. 15, 19552,723,376 Labin Nov. 8, 1955 2,726,332 Arditi et al. Dec. 6, 19552,733,305 Diemer Jan. 31, 1956 2,748,268 Whinnery May 29, 1956 2,760,161Cutler Aug. 21, 1956 OTHER REFERENCES Traveling Wave Tubes, by Hutter etal., Radio Electronic Engineering, April 1954, page 23.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,888,649 May 26, 1959 Edward C. Dench et a1.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 4, line '73, for "leads" read lead column 6, line 34, after"which" strike out "as" column "7', line 23, strike out "attenuation maytake the form of a thin coating of" and insert instead coupling devicemay then be connected to an column 8, line 14, after "of" insert-vapplying an amplitude modulation signal between auxiliary electrode 65and cathode 61 of the electron gun is line 61,- after "and," insert inSigned and sealed this 20th day of' October 1959.

(SEAL) Attest:

KARL H. AXLINE Commissioner of Patents

